Arc Main article: Arc Welding These processes use a welding power supply to establish and maintain an electric arc between the electrode and the material base to melt metals for welding point. They can use either direct (DC) or alternating (AC) current, and consumable or non-consumable electrode. Welding region is sometimes protected by some type of inert or semi-inert, known as the shielding gas and filler is sometimes used as well. [Edit] Power To supply the electrical energy necessary for arc welding, a variety of power sources can be used. The most common welding power supplies are constant current and constant voltage power supply. In arc welding, arc length is directly related to stress, and the amount of heat associated with the current. Direct current power is most often used for manual welding processes such as gas tungsten arc welding and arc welding, as they support a relatively constant current even as the voltage changes. This is important because in manual welding, it can be difficult to hold the electrode very stable, and as a consequence, the arc length and, therefore, stresses tend to fluctuate. Constant voltage power supply to keep the voltage constant and vary the current and, consequently, are most often used for automatic welding, such as gas metal arc welding, flux cored arc welding and arc welding. In these processes, arc length is kept constant, as any fluctuations in the distance between the wire and material resources to quickly fix a large change in current. For example, if the wires and facilities are too close, the current will increase rapidly, which in turn leads to an increase in heat and the tip of the wire to melt, returning it to its original distance of separation [15]. Type of current used also plays an important role in arc welding. Consumable electrode processes such as arc welding and gas metal arc welding generally use direct current, but the electrode can be charged either positively or negatively. When welding, the positively charged anode will have more concentration of heat, and as a consequence, changing the polarity of the electrodes has an influence on the properties of the weld. If the electrode is positively charged, non-precious metals will be hotter, increasing the penetration and welding speed. In addition, the negative electrode leads to the smaller joints [16]. Non-consumable electrode processes, such as gas tungsten arc welding, you can use any type of DC and AC. However, with DC as well as the electrode only creates the arc and does not provide filler material, a positively charged electrode causes shallow welds, while the negatively charged electrode makes deeper welds. [17] Alternating current rapidly moves between these two, resulting in a medium penetrating weld. One disadvantage of AC, the fact that the arc must be re-ignited after every zero crossing, was greeted with the invention of special power units that produce a square wave pattern instead of the normal sine wave, making rapid zero crossings possible and to minimize the impact of the problem [18 ]. [Edit] Processes One of the most common types of arc welding arc welding (SMAW); [19], also known as manual metal arc welding (MMA) welding or stick. An electric current is used to strike an arc between the material and technical base and supplies rod electrode, which is made of steel and coated with flux, which protects the weld area from oxidation and contamination on the production of carbon dioxide (CO2) gas during the welding process. Electrode core itself acts as filler, making it unnecessary to separate the filler [19]. Arc Welding The process is versatile and can be accomplished with relatively inexpensive equipment, making it well suited to shop jobs and field work. [19] [20], the operator can become skilled enough with a modest amount of training and can achieve mastery with experience. Welding times rather slow, as consumable electrodes must be replaced frequently, and because slag, flux residues must be chipped after welding. [19] Furthermore, the process is generally limited to welding ferrous metals, although specific electrodes may weld iron, nickel, aluminum, copper and other metals [20]. Gas metal arc welding (wire), also known as metal inert gas welding, or MIG, is a semi-automatic or automatic process that uses a continuous wire feed as an electrode and inert or semi-inert gas mixture to protect the weld from contamination. Since the electrode is continuous, welding speed is greater than for wire for SMAW [21]. A related process, flux cored arc welding (FCAW), uses similar equipment but uses wire consisting of a steel electrode surrounding the filling of the powder material. This cored wire is more expensive than standard solid wire and can generate a pair and / or slag, but it allows higher welding speed and greater metal penetration [22]. Gas tungsten arc welding (GTAW), or tungsten inert gas (TIG) welding, is a manual welding process that uses non-consumable tungsten electrode, inert or semi-inert gas mixture and a separate filler material. [23] Especially useful for welding thin materials, this method is characterized by a stable arc and high quality welds, but it requires considerable operator skill and can only be accomplished at relatively low speeds. [23] GTAW can be used on virtually all weldable metals, though it is most often applied to stainless steel and light metals. It is often used when quality welds are extremely important, for example, bicycle, aircraft and naval applications. [23], its process, plasma arc welding, also uses a tungsten electrode but uses plasma gas to make the arc. Arc more concentrated than the GTAW arc, making transverse control more critical and thus generally restricting the technique of mechanized process. Because of the stable current, the method can be used in a wider range of material thickness than can GTAW process and it is much faster. It can be applied to all of the same materials as GTAW except magnesium, and automated welding of stainless steel is an important application of the process. Changing the process of plasma cutting, steel cutting process efficient [24]. Terms and definitions (SAW) is a method of high performance welding, in which the arc under the covering layer of flux. This improves the quality of the arc, as the pollutants into the air flow is blocked. Slag, which is formed after welding usually goes by itself and in combination with a continuous wire feed, weld deposition rate is high. Working conditions improved significantly in comparison to other arc welding, because the flow hides the arc and almost no smoke is produced. The process is commonly used in industry, especially for large products, and welded pressure vessels. [25] Other arc welding include atomic hydrogen welding, electroslag welding, Electrogas welding, and stud arc welding [26].